1. Technical Field
The present invention relates to a driving technique for a discharge lamp that is lit according to electric discharge between electrodes.
2. Related Art
A high-intensity discharge lamp such as a high-pressure discharge lamp is used as a light source used for an image display apparatus such as a projector. In such a high-intensity discharge lamp, deterioration of the electrodes worsens according to energization. When the electrodes are deteriorated, it is likely that arc jump, flicker and the like which a light arc generation position moves occur. Usually, when the electrodes are deteriorated, a voltage between the electrodes (a lamp voltage) rises. Therefore, the lamp voltage is detected, a driving condition (a power supply condition) for the high-intensity discharge lamp is changed on the basis of the detected lamp voltage to repair the deteriorated electrodes (see, for example, U.S. Pat. No. 6,232,725).
However, although a power supply condition for use in a state of a higher lamp voltage (a high-voltage side power supply condition) is suitable for repairing the electrodes, if the high-intensity discharge lamp continues to be driven under this condition for a long time, it is likely that a harmful effect such as blackening is caused. Under a power supply condition for use in a state of a lower lamp voltage (a low-voltage side power supply condition), although the harmful effect such as blackening does no occur, the deterioration of the electrodes gradually worsens. This problem is not limited to the high-intensity discharge lamp and is common to various discharge lamps that radiate light according to ark discharge between electrodes.